Nonuniform electric field

Particularly in mass spectrometry, where discharges are used to enhance or produce ions from sample materials, mostly coronas, plasmas, and arcs are used. The gas pressure is normally atmospheric, and the electrodes are arranged to give nonuniform electric fields. Usually, coronas and plasmas are struck between electrodes that are not of similar shapes, complicating any description of the discharge because the resulting electric-field gradients are not uniform between the electrodes. 

The theory and appHcation of SF BDV and COV have been studied in both uniform and nonuniform electric fields (37). The ionization potentials of SFg and electron attachment coefficients are the basis for one set of correlation equations. A critical field exists at 89 kV/ (cmkPa) above which coronas can appear. Relative field uniformity is characterized in terms of electrode radii of curvature. Peak voltages up to 100 kV can be sustained. A second BDV analysis (38) also uses electrode radii of curvature in rod-plane data at 60 Hz, and can be used to correlate results up to 150 kV. With d-c voltages (39), a similarity rule can be used to treat BDV in fields up to 500 kV/cm at pressures of 101—709 kPa (1—7 atm). It relates field strength, SF pressure, and electrode radii to coaxial electrodes having 2.5-cm gaps. At elevated pressures and large electrode areas, a faH-off from this rule appears. The BDV properties ofHquid SF are described in thehterature (40—41). 

Brush discharge A nonuniform electric field between a charged dielectric and a conductor that has a moderate radius of curvature MIE <3 ml... 

Corona A corona is generated when a highly nonuniform electric field of sufficient strength terminates on a conductor that has a small radius of curvature (i.e., a point, wire, or knife-edge). The luminous... 

Wiley, New York, 1973, chap. 14 and chap. 15 (with Crane). Pohl, in Catsim-poolas (ed.). Methods of Cell Separation, vol. I, Plenum Press, New York, 1977, chap. 3. Pohl, Dielectrophoresis The Behavior of Matter in Nonuniform Electric Fields, Cambridge, New York, 1978. 

Substrate and intermediate species adsorb on an electrode surface and orient themselves so that their least hindered sides face the electrode, unless there is another effect such as a polar one. An electrode interface has a layered structure in which a nonuniform electric field (some slope of potential) is generated by polarization of the electrode. An extremely strong electric field of approximately 10 V cm i in the innermost layer might cause a variety of polar effects. For instance, electrochemical one-electron oxidation of o-aminophenol derivatives proceeds adiabatically. On the contrary, the homogeneous reaction is nonadiabatic. This difference in behavior is related to... 

Fig. 13.10. Mechanism of tip sharpening by an electrical field, (a) W atoms on the tip shank walk to the tip apex due to the nonuniform electrical field, (b) A nanotip is formed. (Reproduced from Chen, 1991, with permission.)...

Plazl, I., Pipus, G. and Koloini, T., Microwave heating of the continuous flow catalytic reactor in a nonuniform electric field, AIChE J., 1997, 43, 754. 

As a general conclusion it can be stated that the strip has a nonuniform electrical field, ionic strength, and buffer concentration, but that modification in pH will only occur if these irregularities increase too quickly. In Table 4 the buffers are grouped according to the intended separation. 

DEP is based on a force exerted on a dielectric particle by a nonuniform electric field. The strength of the force depends on the electrical properties... 

Applications of Dielectrophoresis Over the past 20 years the use of DEP has grown rapidly to a point at which it is in use for biological, colloidal, and mineral materials studies and handhng. The effects of nonuniform electric fields are used for handhng particulate matter far more often than is usually recognized. This includes the... 

Moments and polarizabilities can also be obtained by the fixed-charge method [76]. This technique allows for the single-step incorporation of the nonuniform electric field contributions due to gradients and higher order field derivatives. One or more charges are placed around the molecule in regions where the molecular wavefunctions are negligible. It is important that the basis set used for the field-free molecule be the same as that used in the presence of the field and that the molecule basis be adequate to describe any... 

---